This invention relates generally to power line communications (PLC) systems and more particularly, to a power line communication system for transmitting commands and data past capacitor banks of typical power distribution grids.
Electric power supply companies typically have a service person visit customer sites to read an electricity meter at the site to determine the amount of energy consumed for billing purposes. This can be cumbersome and time consuming, particularly when there are many customer sites over a large geographic area.
Automatic Meter Reading (AMR) is the remote collection of consumption data from customers"" utility meters using telephony, radio frequency, power-line and satellite communications technologies. AMR provides water, gas and electric utility-service companies the opportunity to increase operational efficiency, improve customer service, reduce data-collection costs and quickly gather critical information that provides insight to company decision-makers.
Many systems have been proposed for automated meter reading (AMR) operations. Some systems involve, for example, power line or radio communications. Other systems are hybrids, i.e., involve both power line and radio communications. Typically, data and commands can be transmitted between a central station and the electricity meters. Such communication systems enable utilities to easily and quickly obtain energy consumption measurements at many different sites.
Geometric Harmonic Modulation (GHM) of communication signals for transmission on the power line is particularly well suited for AMR applications since GHM signals can be transmitted through power line components such as distribution transformers. GHM is described, for example, in Hershey et al., U.S. Pat. No. 5,519,725, which is assigned to the present assignee. Generally, GHM allocates signaling energy into lobes, or tones, or different frequencies evenly spaced. The GHM signaling waveforms are spread spectrum signals in that the signal bandwidth, i.e., the bandwidth from the lowest frequency tone to the highest, exceeds the information bandwidth conveyed by the GHM transmission.
GHM signals are typically carried on carriers having frequencies above 5 kHz to avoid the large spectral components of the 60 Hz power signal. In addition, higher frequencies are more readily transmitted through the distribution transformers existing in typical power line systems. However, the higher the selected GHM carrier frequency set, the more the GHM signal is attenuated by capacitor banks residing in typical power line systems. Therefore, a need exists for systems and methods which transmit data through power distribution transformers, while overcoming the limitations imposed by capacitor banks in the distribution grid.
The invention provides an aggregator for use in connection with a power distribution network including a power line. The aggregator comprises a receiver, a controller, and a data outbound link. The receiver is coupled to the power line and is configured to receive signals comprising messages, for example geometric harmonic modulation (GHM) signals, from the power line. The controller is coupled to the receiver and to the data outbound link. The controller is configured to provide messages received by the receiver to the data outbound link for transmission by radio frequency energy to a destination, for example a power control station.